Validity and Reliability

• Internal Validity refers to the extent to which the data collected in a study is accurate and reflects the true underlying process.
• Threats to Internal Validity include Researcher Bias, Confounding Variables, Demand Characteristics, Social Desirability Bias, and Mundane Realism.
• Reliability

  The extent to which a test or measure is consistent within itself
• Types of reliability

  • Internal reliability
  • External reliability
• Internal reliability

  The extent to which a test or measure is consistent within itself, e.g. the use of standardised instructions and procedures for all participants
• External reliability

  The extent to which a test produces consistent results over several occasions
• Reliability issues

  • Lack of operationalisation of the variables
  • Order effects in repeated measures design
  • Lack of standardised procedures, inconsistency of measuring tools and an uncontrolled environment
• Dealing with reliability issues

  1. Increasing levels of control in a study

  2. Using standardised procedure, instructions and scientific measuring equipment

  3. Conducting research in a laboratory environment

  4. Counterbalancing to combat order effects
• Measures used to assess reliability

  • Split-half reliability/testing
  • Test-retest reliability
  • Inter-rater reliability
• Split-half reliability/testing

  Involves splitting a participant's test answers in half and seeing whether they got the same or similar scores on the two halves
• Test-retest reliability

  Involves testing and retesting the same participants over time, with the same test, and comparing their scores
• Inter-rater reliability

  Where two or more psychologists produce consistent results by using a standardised procedure, agreed coding system, or correlation of their data